Occurrence and fate of emerging contaminants in urban groundwater. A case study : Barcelona

Ensuring good water quality is becoming a major challenge in urban areas. Urban aquifers may suffer pollution from different recharge sources such as water leakage from sewer and septic systems, seepage from rivers, seawater intrusion, and losses from water supply network among others. As a result, a wide range of organic pollutants are found in urban aquifers. Since these pollutants enter the groundwater environment through the aforementioned sources, their occurrence depends on the transport mechanisms as well as the chemical and biochemical processes that occurred simultaneously. Thus, a proper assessment of groundwater quality requires an understanding of all the processes that affect these pollutants. However, the quantification of these processes is not an easy task. The aims of this thesis are to investigate the occurrence of emerging organic contaminants (EOCs) and the processes that affect them in an urban aquifer. An extensive review including the occurrence and fate of EOCs in Spanish groundwater and the evaluation of potential sources of contamination was carried out. Among organic contaminants found in groundwater, we have analysed pharmaceutically active compounds (PhACs), drugs of abuse (DAs) and personal care products in urban groundwater of Barcelona. The main sources of pollution of EOCs in urban areas are sewer leakage loss and infiltration from waste water treatment plants. Once these contaminants enter the aquifer, their concentrations are affected by numerous processes, including concentration at the source, dilution, adsorption and degradation. Many EOCs are removed from water by transformation or degradation, especially if the water has undergone a broad range of redox states. Therefore, identifying and quantifying the redox processes along a flow line is a key issue. In order to quantify such processes, we have proposed an approach using mixing ratios. The application of environmental isotopes coupled with hydrochemistry data using mixing ratios has provided the isotopic quantification of groundwater recharge sources and the occurrence of redox processes such as sulphate reduction, aerobic respiration and denitrification. The approach enabled us: (1) to quantify the mixing ratios into groundwater (2) to evaluate redox processes.Garantir una bona qualitat de l'aigua s'està convertint en un seriós problema en les zones urbanes. Els aqüífers urbans poden patir contaminació de diverses fonts de recàrrega, com fuites d'aigua de clavegueram i fosses sèptiques, filtracions des dels rius contaminats, intrusió marina, i pèrdues de la xarxa de proveïment d'aigua, entre d'altres. Per això, en els aqüífers urbans es troben diversos contaminants orgànics. La presència i evolució d'aquests contaminants als aqüífers depèn dels mecanismes de transport, així com dels processos químics i bioquímics. Per tant, una correcta avaluació de la qualitat de l'aigua subterrània requereix un enteniment de tots els processos que afecten aquests contaminants. No obstant això, la quantificació d'aquests processos no és una tasca fàcil. Els objectius d'aquesta tesi són investigar la presència de contaminants orgànics emergents (COEs) i els processos que els afecten en un aqüífer urbà. S'ha dut a terme una extensa revisió bibliogràfica de la presència de COEs en les aigües subterrànies d'Espanya, juntament amb l'avaluació de possibles fonts de contaminació. Entre els contaminants orgànics que es troben en les aigües subterrànies, s'han analitzat nombrosos fàrmacs, drogues d'abús i productes de cura personal en l'aigua subterrània urbana de Barcelona. Les principals fonts de contaminació dels COEs en zones urbanes són la pèrdua de les xarxes de clavegueram i els efluents de les estacions depuradores d'aigües residuals. Una vegada que aquests contaminants són presents a l'aqüífer, les seves concentracions es veuen afectades per nombrosos processos, incloent dilució, adsorció i degradació. Molts COEs poden ser eliminats de l'aigua subterrània per processos de transformació o degradació, especialment si l'aqüífer ha passat per diferents estats redox. Per això, la identificació i quantificació dels processos redox a l'aqüífer és una qüestió clau. Per quantificar aquests processos, s'ha proposat un mètode que utilitza les proporcions de mescla. L'aplicació dels isòtops ambientals juntament amb les dades hidroquímiques ha proporcionat la quantificació isotòpica de fonts de recàrrega d'aigua subterrània i l'ocurrència de processos redox, com la sulfato reducció, la respiració aeròbica i desnitrificació. L'ús d'aquestes metodologies ha permès: (1) quantificar les proporcions de barreja en l'aigua subterrània i (2) avaluar els processos redox.Garantizar una buena calidad del agua se está convirtiendo en un gran problema en zonas urbanas. Los acuíferos urbanos pueden sufrir contaminación a través de diversas fuentes de recarga, como fugas de agua de alcantarillado y fosas sépticas, las filtraciones desde los ríos contaminados, intrusión marina, y pérdidas de la red de abastecimiento de agua, entre otros. Por ello, en los acuíferos urbanos se encuentran numerosos contaminantes orgánicos. La presencia y evolución de estos contaminantes en los acuíferos depende de los mecanismos de transporte, así como de los procesos químicos y bioquímicos. Por lo tanto, una correcta evaluación de la calidad del agua subterránea requiere la evaluación de todos los procesos que afectan a estos contaminantes. Sin embargo, la cuantificación de estos procesos no es una tarea fácil. Los objetivos de la presente tesis son determinar la presencia de contaminantes orgánicos emergentes (COEs) y los procesos que los afectan en un acuífero urbano. Se ha llevado a cabo una extensa revisión bibliográfica de la presencia de COEs en las aguas subterráneas de España y la identificación de posibles fuentes de contaminación. Entre los contaminantes orgánicos que se encuentran en las aguas subterráneas, se han analizado numerosos fármacos, drogas de abuso y productos de cuidado personal en las aguas subterráneas urbanas de Barcelona. Las principales fuentes de contaminación de los COEs en zonas urbanas suelen ser las pérdidas de las redes de alcantarillado y los efluentes de las estaciones depuradoras de aguas residuales. Una vez que estos contaminantes están presentes en el acuífero, sus concentraciones se ven afectadas por numerosos procesos, incluyendo dilución, adsorción y degradación. Muchos COEs pueden ser eliminados del agua subterránea por procesos de transformación o degradación, especialmente si en el acuífero ha pasado por diferentes estados redox. Por ello, la identificación y cuantificación de los procesos redox en el acuífero es una cuestión clave. Para cuantificar estos procesos, se ha propuesto un método que utiliza las proporciones de mezcla. La aplicación de los isótopos ambientales junto con los datos hidroquímicos ha proporcionado la cuantificación isotópica de fuentes de recarga de agua subterránea y la ocurrencia de procesos redox, como la sulfato reducción, la respiración aeróbica y desnitrificación. El uso de estas metodologías ha permitido: (1) cuantificar las proporciones de mezcla en el agua subterránea y (2) evaluar los procesos redox

Hydrogeological impact assessment by tunnelling at sites of high sensitivity

A tunnel for the High Speed Train (HST) was constructed in Barcelona with an Earth Pressure Balance (EPB) Tunnel Boring Machine (TBM). The tunnel crosses Barcelona and passes under some famous landmarks such as the Sagrada Familia and the Casa Mill Both monuments are UNESCO world heritage sites and a committee appointed by the UNESCO acted as external observers during the construction. Concerns about soil settlements and the hydrogeological impacts of the construction were raised. These concerns were addressed during the design stage to forestall any unexpected events. The methodology consisted of 1) characterising the geology in detail, 2) predicting the impacts caused in the aquifer, 3) predicting the soil displacements due to water table oscillations produced by the construction, and 4) monitoring the evolution of groundwater and soil settlements. The main estimated impact on groundwater was a moderate barrier effect. The barrier effect, the magnitude of which matched the predictions, was detected during construction. The monitoring of soil settlements revealed short and long term movements. The latter movements matched the analytical predictions of soil displacements caused by the groundwater oscillations. This paper proposes a realistic procedure to estimate impacts on groundwater during tunnel construction with an EPB. Our methodology will considerably improve the construction of tunnels in urban areas. (C) 2015 Elsevier B.V. All rights reserved.Peer ReviewedPostprint (author's final draft

Potential uses of pumped urban groundwater. A case study in Sant Adrià del Besòs (Spain)

peer reviewedUrban groundwater has been over-exploited during the past, mainly for industrial uses, and it now tends to be reduced or abandoned due to pollution and/or changes in land use. The use and the subsequent disuse of groundwater resulted in rising water tables that damage underground structures (e.g., building basements and underground car parks and tunnels), leading to additional pumping in urban areas. This is the case of the underground parking lot of Sant Adrià del Besòs (NE Spain), where large amounts of urban groundwater are pumped to avoid seepage problems. The question that arises here is if this pumped groundwater can be used for other purposes (e.g., drinking water and urban irrigation) instead of wasting this valuable resource. To answer this question, it is necessary to quantify the groundwater recharge and to assess the evolution of ground-water quality in order to properly identify its potential uses. The limiting factor to define the uses of this resource is the groundwater quality because ammonium and some metals (iron and manganese) are present at high concentrations. Hence, further treatment would be needed to meet drinking water requirements. The pumped groundwater could also be used for supplying the ecological river flow and/or for mitigating seawater intrusion problems. Currently, only a small amount of this urban groundwater is used for cleaning public areas and watering public gardens. This situation highlighted the urgent need to manage this resource in a responsible and more efficient manner, especially in moments of high water demand such as drought periods

Dynamics and emissions of N2O in groundwater: A review

peer reviewedThis work reviews the concentrations, the dynamics and the emissions of nitrous oxide (N2O) in groundwater. N2O is an important greenhouse gas (GHG) and the primary stratospheric ozone depleting substance. The major anthropogenic source that contributes to N2O generation in aquifers is agriculture because the use of fertilizers has led to the widespread groundwater contamination by inorganic nitrogen (N) (mainly nitrate, NO3−). Once in the aquifer, this inorganic N is transported and affected by several geochemical processes that produce and consume N2O. An inventory of dissolved N2O concentrations is presented and the highest dissolved concentration is about 18.000 times higher than air-equilibrated water (up to 4004 μg N L-1). The accumulation of N2O in groundwater is mainly due to denitrification and to lesser extent to nitrification. Their occurrence depend on the geochemical (e.g., NO3−, dissolved oxygen, ammonium and dissolved organic carbon) as well as hydrogeological parameters (e.g., groundwater table fluctuations and aquifer permeability). The coupled understanding of both parameters is necessary to gain insight on the dynamics and the emissions of N2O in groundwater. Overall, groundwater indirect N2O emissions seem to be a minor component of N2O emissions to the atmosphere. Further research might be devoted to evaluate the groundwater contribution to the indirect emissions of N2O because this will help to better constraint the N2O global budget and, consequently, the N budget

QUANTIFYING CHEMICAL REACTIONS BY USING MIXING ANALYSIS IN GROUNDWATER-RIVER INTERFACE

This work is motivated by a sound understanding of the chemical processes that affect the organic pollutants in an urban aquifer. Urban aquifers may suffer pollution from different recharge sources such as leakage from sewer and septic systems, seepage from rivers, seawater intrusion, and losses from water supply network. As a result, a wide range of organic pollutants are found in urban aquifers (Fig. 1). Since these pollutants reach groundwater environment, their occurrence depends on simultaneous transport and biogeochemical processes. However, the quantification of these processes is not an easy task. The objective of this work is to propose an approach to quantify the chemical processes that occurs when river water infiltrates an aquifer

Occurrence of greenhouse gases (CO2, N2O and CH4) in groundwater of the Walloon Region (Belgium)

Carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) can be indirectly transferred to the atmosphere through groundwater discharge into surface water bodies such as rivers. However, these emissions are poorly evaluated and highly uncertain. The aim of this work is identify the hydrogeological contexts (alluvial, sandstone, chalk and limestone aquifers) and in situ conditions which are most conducive to the generation and occurrence of GHGs in groundwater at a regional scale. To this end, CO2, CH4 and N2O concentrations as well as major and minor elements were monitored (n=37 samples) in two field campaigns (09/2014 and 03/2015) in 15 groundwater bodies of the Walloon Region (Belgium). This preliminary work, which was presented in the 42st IAH conference (Rome, Italy), shown that GHG concentrations range from 5,160 to 47,544 ppm from the partial pressure of CO2 and from 0 to 1,064 nmol/L and 1 to 5,637 nmol/L for CH4 and N2O respectively. Overall, groundwater was supersaturated in GHGs with respect to atmospheric equilibrium, suggesting that groundwater contribute to the atmospheric GHGs budget. A third sampling campaign is carried out in 2016 including around 60 new groundwater samples. The combination of the results of the three campaigns allows: (1) reducing the uncertainties related to indirect emissions of GHG through groundwater-surface water interaction and (2) contributing to a better understanding of the occurrence of GHGs in aquifers. New results will be presented and discussed in detail in the presentation

Modelling of the EPB TBM shield tunnelling advance as a tool for geological characterization

One of the main causes of problems during the construction of tunnels with tunnel boring machines (TBMs) is a lack of characterization of the soil. Both geological and hydrogeological characterizations are essential to avoid unexpected events. The advance of TBMs produces groundwater oscillations due to hydraulic and mechanical effects. The magnitude of these oscillations depends on the characteristics of the soil and on the ‘‘parameters” of the TBM (e.g., earth pressures, penetration). Given that the impact caused in the groundwater could be estimated numerically, this paper proposes to use hydrogeological models based on the parameters of the TBM to validate or improve the previous geological characterization. This procedure was tested by modelling the advance of a TBM-type earth pressure balance (EPB) at a real site. This study arose during the construction of the tunnel for the high speed train in Barcelona. The previous geological characterization revealed a vertical fault whose exact position was unknown. The advance of the EPB was modelled to validate the previous characterization and to locate the fault. The numerical model included a detailed geology and hydrogeology of the study site and the parameters of the EPB. Note that the parameters of the EPB used in the model were more related to the groundwater response. These were determined statistically from all of the measures taken by the machine. Given the results obtained, hydrogeological modelling of EPBs was revealed to be a useful tool to validate previous characterizations, both the geological and the hydrogeological, and to determine the position of some geological structures, such as faults

Isotopic composition of nitrogen species in groundwater under agricultural areas: A review

This work reviews applications of stable isotope analysis to the studies of transport and transformation of N species in groundwater under agricultural areas. It summarizes evidence regarding factors affecting the isotopic composition of NO3−, NH4+ and N2O in subsurface, and discusses the use of 11B, 18O, 13C, 34S, 87Sr/86Sr isotopes to support the analysis of δ15N values. The isotopic composition of NO3−, NH4+ and N2O varies depending on their sources and dynamics of N cycle processes. The reported δ15N-NO3− values for sources of NO3− are: soil organic N – +3‰–+8‰, mineral fertilizers – −8‰–+7‰; manure/household waste – +5‰ to +35‰. For NH4+ sources, the isotopic signature ranges are: organic matter – +2.4–+4.1‰, rainwater – −13.4–+2.3‰, mineral fertilizers –−7.4–+5.1‰, householdwaste –+5–+9‰; animalmanure–+8–+11‰. ForN2O, isotopic composition depends on isotopic signatures of substrate pools and reaction rates. δ15Nvalues of NO3− are influenced by fractionation effects occurring during denitrification (ɛ=5–40‰), nitrification (ɛ=5–35‰) and DNRA (ɛ not reported). The isotopic signature of NH4+ is also affected by nitrification and DNRA as well as mineralization (ɛ=1‰), sorption (ɛ=1–8‰), anammox (ɛ=4.3–7.4‰) and volatilization (ɛ=25‰). As for theN2O, production of N2O leads to its depletion in 15N, whereas consumption – to enrichment in 15N. The magnitude of fractionation effects occurring during the considered processes depends on temperature, pH, DO, C/NO3− ratio, size of the substrate pool, availability of electron donors, water content in subsoil, residence time, land use, hydrogeology. While previous studies have accumulated rich data on isotopic composition of NO3− in groundwater, evidence remains scarce in the cases of NH4+ and N2O. Further research is required to consider variability of δ15N-NH4+ and δ15N-N2O in groundwater across agricultural ecosystems.H2020 ITN INSPIRATIO